Aircraft gas turbine engines include fan, compressor, and turbine rotor blades which are typically removably mounted to supporting rotor disks. The rotor blades include various circumferential or axial dovetails which are supported in complementary circumferential or axial dovetail slots formed in the rotor disks. Axial dovetails are readily assembled to their respective rotor disks by merely axially sliding the dovetail into the rotor disk, with disassembly thereof being prevented by conventional forward and aft blade retainers.
In order to install circumferential dovetails, a loading slot is required so that the dovetails may be initially radially inserted into the loading slot and then slid circumferentially into position into the dovetail slot. Since the loading slot is not capable of providing any radial retention force, the circumferential dovetails are typically sized for having circumferential spacing therebetween which is typically on the order of the circumferential extent of the loading slot itself. Upon insertion of the last circumferential dovetail into the loading slot, all the blades are circumferentially indexed so that no circumferential dovetail is positioned at the loading slot, with adjacent circumferential dovetails straddling the loading slot for ensuring the radial retention thereof and effective transfer of centrifugal forces from the blades to the disk during operation.
In one type of engine design, fan blades may have a low radius ratio, which is the ratio between the inner diameter to the outer diameter of the flowpath typically measured at the blade platform and tip, that results in a relatively small perimeter of the supporting disk. This increases the difficulty of carrying centrifugal loads from the blades and into the disk with acceptably low stress. Low radius ratio blades are therefore typically formed integrally with the rotor disk, from a common forging for example, for ensuring relatively low stresses during operation and a suitable useful life thereof. However, individual blades are therefore not readily removable since cutting thereof would be required.
It is desirable to have individually removable rotor blades in a low radius ratio blade configuration with acceptable retention stresses therein during operation.